1 IPC interface (interprocess communication)
2 ==========================================
3 Michael Stapelberg <michael+i3@stapelberg.de>
6 This document describes how to interface with i3 from a separate process. This
7 is useful for example to remote-control i3 (to write test cases for example) or
8 to get various information like the current workspaces to implement an external
11 The method of choice for IPC in our case is a unix socket because it has very
12 little overhead on both sides and is usually available without headaches in
13 most languages. In the default configuration file, no ipc-socket path is
14 specified and thus no socket is created. The standard path (which +i3-msg+ and
15 +i3-input+ use) is +/tmp/i3-ipc.sock+.
17 == Establishing a connection
19 To establish a connection, simply open the IPC socket. The following code
20 snippet illustrates this in Perl:
22 -------------------------------------------------------------
24 my $sock = IO::Socket::UNIX->new(Peer => '/tmp/i3-ipc.sock');
25 -------------------------------------------------------------
27 == Sending messages to i3
29 To send a message to i3, you have to format in the binary message format which
30 i3 expects. This format specifies a magic string in the beginning to ensure
31 the integrity of messages (to prevent follow-up errors). Afterwards follows
32 the length of the payload of the message as 32-bit integer and the type of
33 the message as 32-bit integer (the integers are not converted, so they are
34 in native byte order).
36 The magic string currently is "i3-ipc" and will only be changed when a change
37 in the IPC API is done which breaks compatibility (we hope that we don’t need
40 Currently implemented message types are the following:
43 The payload of the message is a command for i3 (like the commands you
44 can bind to keys in the configuration file) and will be executed
45 directly after receiving it. There is no reply to this message.
47 Gets the current workspaces. The reply will be a JSON-encoded list of
48 workspaces (see the reply section).
50 Subscribes your connection to certain events. See <<events>> for a
51 description of this message and the concept of events.
53 Gets the current outputs. The reply will be a JSON-encoded list of outputs
54 (see the reply section).
56 So, a typical message could look like this:
57 --------------------------------------------------
58 "i3-ipc" <message length> <message type> <payload>
59 --------------------------------------------------
62 ------------------------------------------------------------------------------
63 00000000 69 33 2d 69 70 63 04 00 00 00 00 00 00 00 65 78 |i3-ipc........ex|
64 00000010 69 74 0a |it.|
65 ------------------------------------------------------------------------------
67 To generate and send such a message, you could use the following code in Perl:
68 ------------------------------------------------------------
69 sub format_ipc_command {
72 # Get the real byte count (vs. amount of characters)
73 { use bytes; $len = length($msg); }
74 return "i3-ipc" . pack("LL", $len, 0) . $msg;
77 $sock->write(format_ipc_command("exit"));
78 ------------------------------------------------------------
80 == Receiving replies from i3
82 Replies of i3 usually consist of a simple string (the length of the string
83 is the message_length, so you can consider them length-prefixed) which in turn
84 contain the JSON serialization of a data structure. For example, the
85 GET_WORKSPACES message returns an array of workspaces (each workspace is a map
86 with certain attributes).
90 The reply format is identical to the normal message format. There also is
91 the magic string, then the message length, then the message type and the
94 The following reply types are implemented:
97 Confirmation/Error code for the COMMAND message.
99 Reply to the GET_WORKSPACES message.
101 Confirmation/Error code for the SUBSCRIBE message.
103 Reply to the GET_OUTPUTS message.
107 The reply consists of a single serialized map. At the moment, the only
108 property is +success (bool)+, but this will be expanded in future versions.
115 === GET_WORKSPACES reply
117 The reply consists of a serialized list of workspaces. Each workspace has the
118 following properties:
121 The logical number of the workspace. Corresponds to the command
122 to switch to this workspace.
124 The name of this workspace (by default num+1), as changed by the
125 user. Encoded in UTF-8.
127 Whether this workspace is currently visible on an output (multiple
128 workspaces can be visible at the same time).
130 Whether this workspace currently has the focus (only one workspace
131 can have the focus at the same time).
133 Whether a window on this workspace has the "urgent" flag set.
135 The rectangle of this workspace (equals the rect of the output it
136 is on), consists of x, y, width, height.
138 The video output this workspace is on (LVDS1, VGA1, …).
176 The reply consists of a single serialized map. The only property is
177 +success (bool)+, indicating whether the subscription was successful (the
178 default) or whether a JSON parse error occurred.
185 === GET_OUTPUTS reply
187 The reply consists of a serialized list of outputs. Each output has the
188 following properties:
191 The name of this output (as seen in +xrandr(1)+). Encoded in UTF-8.
193 Whether this output is currently active (has a valid mode).
194 current_workspace (integer)::
195 The current workspace which is visible on this output. +null+ if the
196 output is not active.
198 The rectangle of this output (equals the rect of the output it
199 is on), consists of x, y, width, height.
207 "current_workspace": 4,
218 "current_workspace": 1,
233 To get informed when certain things happen in i3, clients can subscribe to
234 events. Events consist of a name (like "workspace") and an event reply type
235 (like I3_IPC_EVENT_WORKSPACE). The events sent by i3 are in the same format
236 as replies to specific commands.
238 Caveat: As soon as you subscribe to an event, it is not guaranteed any longer
239 that the requests to i3 are processed in order. This means, the following
240 situation can happen: You send a GET_WORKSPACES request but you receive a
241 "workspace" event before receiving the reply to GET_WORKSPACES. If your
242 program does not want to cope which such kinds of race conditions (an
243 event based library may not have a problem here), I advise to create a separate
244 connection to receive events.
246 === Subscribing to events
248 By sending a message of type SUBSCRIBE with a JSON-encoded array as payload
249 you can register to an event.
252 ---------------------------------
254 payload: [ "workspace", "focus" ]
255 ---------------------------------
260 Sent when the user switches to a different workspace, when a new
261 workspace is initialized or when a workspace is removed (because the
262 last client vanished).
266 This event consists of a single serialized map containing a property
267 +change (string)+ which indicates the type of the change ("focus", "init",
271 ---------------------
272 { "change": "focus" }
273 ---------------------
277 For some languages, libraries are available (so you don’t have to implement
278 all this on your own). This list names some (if you wrote one, please let me
282 i3 includes a headerfile +i3/ipc.h+ which provides you all constants.
283 However, there is no library yet.
285 http://github.com/badboy/i3-ipc
287 http://search.cpan.org/search?query=AnyEvent::I3